Liquid crystal display device

ABSTRACT

In one embodiment, a liquid crystal display device comprises a first and second substrates and a liquid crystal layer. The first substrate comprises subpixels, first and second common electrodes, and a pixel electrode. Each of the subpixels comprises an axial area, branch areas, and gap areas. The second edge comprises concave portions. The axial and branch areas are areas in which the second common electrode is not present, and the pixel electrode is present. The gap areas are areas in which the second common electrode is present. The concave portions are areas in which the second common electrode and the pixel electrode are not present, and the first common electrode is present.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 15/848,308 filedDec. 20, 2017, and claims the benefit of priority under 35 U.S.C. § 119from Japanese Patent Application No. 2017-007599 filed Jan. 19, 2017,the entire contents of each of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a liquid crystaldisplay device.

BACKGROUND

A liquid crystal display device in an in-plane switching (IPS) mode isknown as an example of a display device. The liquid crystal displaydevice in an IPS mode comprises a pair of substrates facing each othervia a liquid crystal layer. One of the substrates comprises a pixelelectrode and a common electrode. The alignment of the liquid crystalmolecules of the liquid crystal layer is controlled using the lateralelectric field generated between the electrodes. In IPS modes, a liquidcrystal display device in a fringe-field switching (FFS) mode has beenput to practical use. In the liquid crystal display device in an FFSmode, a pixel electrode and a common electrode are provided in differentlayers, and the fringe electric field generated between the electrodesis used to control the alignment of liquid crystal molecules.

Apart from the above, the following liquid crystal display device issuggested. In the liquid crystal display device, a pixel electrode and acommon electrode are provided in different layers. A slit is provided inthe electrode closer to a liquid crystal layer than the other electrode.The liquid crystal molecules near the both sides of the slit in thewidth direction are rotated in opposite directions. This liquid crystaldisplay device is a type of FFS mode. However, the form of the rotationof the liquid crystal molecules of this liquid crystal display device isclearly different from that of the conventional FFS mode which has beenwidely known. This mode can increase the speed of response and improvethe stability of alignment in comparison with the conventional FFS mode.Hereinafter, the structure of this type of liquid crystal display deviceis called a high-speed response mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the schematic structure of adisplay device according to a first embodiment.

FIG. 2 shows the schematic equivalent circuit of the display deviceaccording to the first embodiment.

FIG. 3 shows an example of the cross-sectional surface of the displaydevice according to the first embodiment.

FIG. 4 is a plan view schematically showing an example of a subpixelaccording to the first embodiment.

FIG. 5A is a schematic plan view of the first common electrode shown inFIG. 4.

FIG. 5B is a schematic plan view of the pixel electrode shown in FIG. 4.

FIG. 5C is a schematic plan view of the second common electrode shown inFIG. 4.

FIG. 6 is a partial enlarged view of the axial area and each branch areashown in FIG. 4.

FIG. 7 shows the alignment state of liquid crystal molecules in anoff-state.

FIG. 8 shows the alignment state of liquid crystal molecules in anon-state.

FIG. 9 shows a comparison example of the first embodiment.

FIG. 10 shows a comparison example of the first embodiment.

FIG. 11 shows a modification example of the first embodiment.

FIG. 12 shows an example of the cross-sectional surface of a displaydevice according to a second embodiment.

FIG. 13 is a plan view schematically showing an example of a subpixelaccording to the second embodiment.

FIG. 14A is a schematic plan view of the first pixel electrode shown inFIG. 13.

FIG. 14B is a schematic plan view of the common electrode shown in FIG.13.

FIG. 14C is a schematic plan view of the second pixel electrode shown inFIG. 13.

FIG. 15 shows a modification example of the second embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a liquid crystal display devicecomprises a first substrate; a second substrate; and a liquid crystallayer provided between the first substrate and the second substrate, andincluding liquid crystal molecules. The first substrate comprises aplurality of subpixels; a first common electrode having commonpotential; a second common electrode between the first common electrodeand the liquid crystal layer, and having the common potential; and apixel electrode between the first common electrode and the second commonelectrode, provided for each of the subpixels and having pixelpotential. Each of the subpixels comprises an axial area comprisingfirst and second edges arranged in a first direction, and extending in asecond direction intersecting the first direction; a plurality of branchareas extending from the first edge of the axial area in the firstdirection; and a plurality of gap areas between the branch areas. Thesecond edge comprises a plurality of concave portions arranged in thesecond direction. The axial area and the branch areas are areas in whichthe second common electrode is not present, and the pixel electrode ispresent. The gap areas are areas in which the second common electrode ispresent. The concave portions are areas in which the second commonelectrode and the pixel electrode are not present, and the first commonelectrode is present.

According to another embodiment, a liquid crystal display devicecomprises a first substrate; a second substrate; and a liquid crystallayer provided between the first substrate and the second substrate, andincluding liquid crystal molecules. The first substrate comprises aplurality of subpixels; a first pixel electrode provided for each of thesubpixels, and having pixel potential; a second pixel electrode betweenthe first pixel electrode and the liquid crystal layer, provided foreach of the subpixels, and having pixel potential; and a commonelectrode between the first pixel electrode and the second pixelelectrode, and having common potential. Each of the subpixels comprisesan axial area comprising first and second edges arranged in a firstdirection, and extending in a second direction intersecting the firstdirection; a plurality of branch areas extending from the first edge ofthe axial area in the first direction; and a plurality of gap areasbetween the branch areas. The second edge comprises a plurality ofconvex portions arranged in the second direction. The branch areas areareas in which the second pixel electrode is present. The gap areas areareas in which the second pixel electrode is not present, and the commonelectrode is present. The convex portions are areas in which the secondpixel electrode and the common electrode are not present, and the firstpixel electrode is present.

The above structures allow the provision of a liquid crystal displaydevice in high-speed response mode in which the stability of alignmenthas been further improved.

Embodiments will be described with reference to the accompanyingdrawings.

The disclosure is merely an example, and proper changes in keeping withthe spirit of the invention, which are easily conceivable by a person ofordinary skill in the art, come within the scope of the invention as amatter of course. In addition, in some cases, in order to make thedescription clearer, the drawings show schematic illustration ratherthan as an accurate representation of what is implemented. However, suchschematic illustration is merely exemplary, and in no way restricts theinterpretation of the invention. In the drawings, reference numbers ofcontinuously arranged elements equivalent or similar to each other areomitted in some cases. In addition, in the specification and drawings,structural elements which function in the same or a similar manner tothose described in connection with preceding drawings are denoted bylike reference numbers, detailed description thereof being omittedunless necessary.

In this specification, the phrases “∝ includes A, B or C”, “∝ includesone of A, B and C” and “∝ includes an element selected from a groupconsisting of A, B and C” do not exclude a case where ∝ includes aplurality of combinations of A to C unless specified. Further, thesephrases do not exclude a case where ∝ includes other elements.

In this specification, the expressions “first” “second” and “third” of“the first member, the second member and the third member” are merelyordinal numbers used to explain the elements for the sake ofconvenience. Thus, the expression “A comprises the third member”includes a case where A does not comprise the first member and thesecond member unless otherwise specified.

In each embodiment, a transmissive type liquid crystal display device isdisclosed as an example of a liquid crystal display device. However,each embodiment does not prevent application of individual technicalideas disclosed in the embodiment to other types of display devices.Other types of display devices are assumed to include, for example, areflective type liquid crystal display device which displays an imageusing outside light, and a liquid crystal display device having both thetransmissive function and the reflective function.

First Embodiment

FIG. 1 is a perspective view showing the schematic structure of a liquidcrystal display device (hereinafter referred to as a display device) 1according to a first embodiment. The display device 1 may be used forvarious devices such as a smartphone, a tablet, a mobile phone, apersonal computer, a television receiver, a vehicle-mounted device, agame console and a wearable device.

The display device 1 comprises a display panel 2, a backlight 3 facingthe display panel 2, a driver IC 4 which drives the display panel 2, acontrol module 5 which controls the operation of the display panel 2 andthe backlight 3, and flexible circuit boards FPC1 and FPC2 whichtransmit a control signal to the display panel 2 and the backlight 3.

In the present embodiment, a first direction D1 is the direction inwhich each branch area 40 extends as described later. A second directionD2 is the direction in which an axial area 30 extends as describedlater. In FIG. 1, the first direction D1 is also applicable to thedirection along the short sides of the display panel 2. The seconddirection D2 is also applicable to, for example, the direction along thelong sides of the display panel 2. In the example shown in FIG. 1, thefirst direction D1 intersects the second direction D2 at right angle.However, the first and second directions D1 and D2 may intersect atanother angle.

The display panel 2 comprises first and second substrates SUB1 SUB2facing each other, and a liquid crystal layer (the liquid crystal layerLC described later) provided between the first substrate SUB1 and thesecond substrate SUB2. The display panel 2 comprises a display area DAwhich displays an image. The display panel 2 comprises, for example, aplurality of pixels PX arranged in matrix in the first and seconddirections D1 and D2 in the display area DA.

FIG. 2 shows the schematic equivalent circuit of the display device 1.The display device 1 comprises a first driver DR1, a second driver DR2,a plurality of scanning signal lines G connected to the first driverDR1, and a plurality of video signal lines S connected to the seconddriver DR2. The scanning signal lines G extend in the first direction D1and are arranged in the second direction D2 in the display area DA. Inthe display area DA, the video signal lines S extend in the seconddirection D2, are arranged in the first direction D1, and intersect thescanning signal lines G.

Each pixel PX comprises a plurality of subpixels SP. In the presentembodiment, it is assumed that each pixel PX includes a subpixel SPRcorresponding to red, a subpixel SPG corresponding to green and asubpixel SPB corresponding to blue. However, each pixel PX may furtherinclude, for example, a subpixel SP corresponding to white, or mayinclude a plurality of subpixels SP corresponding to the same color. Inthis disclosure, each subpixel may be simply referred to as a pixel.

Each subpixel SP comprises a switching element SW, a pixel electrode PEand a common electrode CE facing the pixel electrode PE. The commonelectrode CE is formed over a plurality of subpixels SP. Commonpotential is applied to the common electrode CE. Each switching elementSW is connected to a corresponding scanning signal line G, acorresponding video signal line S and a corresponding pixel electrodePE. Each pixel electrode PE is electrically connected to a correspondingvideo signal line S via a corresponding switching element SW.

The first driver DR1 supplies a scanning signal to the scanning signallines G in series. The second driver DR2 selectively supplies a videosignal to the video signal lines S. When a scanning signal is suppliedto a scanning signal line G corresponding to a switching element SW, andfurther when a video signal is supplied to the video signal line Sconnected to the switching element SW, pixel potential is applied to acorresponding pixel electrode PE in accordance with the video signal. Atthis time, an electric field is generated between the pixel electrode PEand the common electrode CE. By this electric field, the alignment ofthe liquid crystal molecules of the liquid crystal layer LC is changedfrom the initial alignment state where no voltage is applied. By thisoperation, an image is displayed in the display area DA.

FIG. 3 shows a part of the cross-sectional surface of the display device1. FIG. 3 shows the schematic cross-sectional surface of a subpixel SP.

The first substrate SUB1 comprises a first insulating substrate 10 suchas a phototransmissive glass substrate or resinous substrate. The firstinsulating substrate 10 comprises a first main surface 10A facing thesecond substrate SUB2, and a second main surface 10B opposite to thefirst main surface 10A. The first substrate SUB1 further comprises theswitching element SW, the pixel electrode PE, the common electrode CE, afirst insulating layer 11, a second insulating layer (first dielectriclayer) 12, a third insulating layer (second dielectric layer) 13, and afirst alignment film 14. In the present embodiment, the common electrodeCE includes a first common electrode CE1 and a second common electrodeCE2. The same common potential is applied to the first and second commonelectrodes CE1 and CE2.

The switching element SW is provided on the first main surface 10A ofthe first insulating substrate 10, and is covered with the firstinsulating layer 11. In FIG. 3, the illustration of the scanning signallines G or the video signal lines S is omitted. Moreover, in FIG. 3, theswitching element SW is simplified. In the actual device, the firstinsulating layer 11 includes a plurality of layers, and the switchingelement SW includes a semiconductor layer and various electrodes formedin these layers.

The first common electrode CE1 is formed on the first insulating layer11. The first common electrode CE1 is covered with the second insulatinglayer 12. The pixel electrode PE is formed on the second insulatinglayer 12. The pixel electrode PE is connected to the switching elementSW via a contact hole H11 penetrating the first and second insulatinglayers 11 and 12 and an aperture A11 provided in the first commonelectrode CE1.

The pixel electrode PE is covered with the third insulating layer 13.The second common electrode CE2 is formed on the third insulating layer13. The second common electrode CE2 is connected to the first commonelectrode CE1 via a contact hole H12 penetrating the second and thirdinsulating layers 12 and 13. The first alignment film 14 covers thesecond common electrode CE2 and the third insulating layer 13, and is incontact with the liquid crystal layer LC. The pixel electrode PE and thefirst and second common electrodes CE1 and CE2 can be formed of atransparent conductive material such as indium tin oxide (ITO).

The second common electrode CE2 comprises an aperture A12. The pixelelectrode PE and the first common electrode CE1 are also formed at aposition overlapping the aperture A12 as seen in plan view.

The second substrate SUB2 comprises a second insulating substrate 20such as a phototransmissive glass substrate or resinous substrate. Thesecond insulating substrate 20 comprises a first main surface 20A facingthe first substrate SUB1, and a second main surface 20B opposite to thefirst main surface 20A. The second substrate SUB2 further comprises alight-shielding layer 21, a color filter 22, an overcoat layer 23 and asecond alignment film 24. At least one of the light-shielding layer 21and the color filter 22 may be provided in the first substrate SUB1.

The light-shielding layer 21 is provided at the boundaries of thesubpixel SP as seen in plan view. By the light-shielding layer 21provided in the above manner, a pixel aperture PA which substantiallycontributes to image display is formed. The color filter 22 covers thefirst main surface 20A of the second insulating substrate 20 and thelight-shielding layer 21. For example, a color corresponding to thesubpixel SP is applied to the color filter 22. The overcoat layer 23covers the color filter 22 and planarizes the surface of the colorfilter 22. The second alignment film 24 covers the overcoat layer 23,and is in contact with the liquid crystal layer LC.

The first and second alignment films 14 and 24 have a function forcausing the liquid crystal molecules included in the liquid crystallayer LC to be aligned in the initial alignment direction. For example,the first and second alignment films 14 and 24 are optical alignmentfilms which underwent optical alignment treatment for adding anisotropyby irradiating a polymer film such as polyimide with ultraviolet light.Alternatively, the first and second alignment films 14 and 24 may berubbing alignment films which underwent rubbing treatment. One of thefirst and second alignment films 14 and 24 may be an optical alignmentfilm, and the other one may be a rubbing alignment film.

In the example of FIG. 3, a first optical element OD1 including a firstpolarizer PL1 is provided on the second main surface 10B of the firstinsulating substrate 10. A second optical element OD2 including a secondpolarizer PL2 is provided on the second main surface 20B of the secondinsulating substrate 20.

FIG. 4 is a plan view schematically showing an example of a subpixel SP.FIG. 5A, FIG. 5B and FIG. 5C are the schematic plan views of the firstcommon electrode CE1, the pixel electrode PE and the second commonelectrode CE2 shown in FIG. 4, respectively. The subpixel SP shown inFIG. 4 corresponds to the area surrounded by two scanning signal lines G(G1 and G2) adjacent to each other in the second direction D2 and twovideo signal lines S (S1 and S2) adjacent to each other in the firstdirection D1. The elements such as the above switching element SW areomitted in the figure.

As shown in FIG. 5A, the first common electrode CE1 comprises theaperture A11. The contact hole H1 is provided at a position overlappingthe aperture A11 as seen in plan view.

In the examples of FIG. 4 and FIG. 5B, the pixel electrode PE isprovided within the area surrounded by the scanning signal lines G1 andG2 and the video signal lines S1 and S2. However, a part of the pixelelectrode PE may extend to the outside of the area. As shown in FIG. 4and FIG. 5B, the pixel electrode PE comprises a concave portion R nearthe intersection between the scanning signal line G1 and the videosignal line S1. The contact hole H12 for connecting the first and secondcommon electrodes CE1 and CE2 is provided in the concave portion R. Thecontact hole H12 may not be provided in all the subpixels SP. Even wheneach contact hole H12 is provided for a corresponding group of subpixelsSP, the conduction of the first and second common electrodes CE1 and CE2can be ensured. The first and second common electrodes CE1 and CE2 maybe electrically connected in a peripheral area SA.

For example, the first common electrode CE1 overlaps substantially theentire area of the pixel electrode PE and the second common electrodeCE2. However, the pixel electrode PE and the second common electrode CE2may comprise a portion which does not overlap the first common electrodeCE1.

As shown in FIG. 4 and FIG. 5C, the second common electrode CE2comprises the aperture A12. The aperture A12 includes the axial area 30,a plurality of branch areas 40 and an extension area 50. The axial area30 extends in the second direction D2, and is close to the video signalline S2. The axial area 30 comprises a first edge E1 on the video signalline S1 side, and a second edge E2 on the video signal line S2 side.

Each branch area 40 extends in the first direction D1 from the firstedge E1 of the axial area 30 to the video signal line S1. For example,each branch area 40 has a shape tapering toward the distal end. A gaparea 60 is formed between two branch areas 40 adjacent to each other inthe second direction D2. The extension area 50 extends in the seconddirection D2 along the second edge E2 of the axial area 30.

In the example of FIG. 4, all the branch areas 40 have the same shape,and are arranged at regular pitches in the second direction D2.Similarly, all the gap areas 60 have the same shape, and are arranged atregular pitches in the second direction D2. However, all the branchareas 40 or all the gap areas 60 may not have the same shape, or may notbe arranged at regular pitches. One or some of them may have a differentshape. Some of them may be arranged at a different pitch.

In the example of FIG. 4, the end portions of the axial area 30 in thesecond direction D2 are aligned with the end portions of the extensionarea 50 in the second direction D2. However, on at least one of thescanning signal line G1 side and the scanning signal line G2 side, theend potion of the axial area 30 may not be aligned with the end portionof the extension area 50.

The pixel aperture PA indicated with the alternate long and short dashline overlaps each branch area 40 and each gap area 60. In the exampleof FIG. 4, none of the distal and proximal portions of the branch areas40 and the gap areas 60 is included in the pixel aperture PA. In otherwords, the distal and proximal portions of each branch area 40 and eachgap area 60 overlap the light-shielding layer 21. The axial area 30, theextension area 50, the scanning signal lines G1 and G2, the video signallines S1 and S2, and the contact holes H11 and H12 also overlap thelight-shielding layer 21. However, the light-shielding layer 21 may notoverlap at least a part of the axial area 30 and the extension area 50.The light-shielding layer 21 may not overlap at least one of the distalportion and the proximal portion of each branch area 40 and each gaparea 60.

The second edge E2 of the axial area 30 comprises a plurality of concaveportions 70 arranged in the second direction D2. Each concave portion 70is aligned with a corresponding branch area 40 in the first directionD1. For example, the center of each branch area 40 in the seconddirection D2 may match the center of a corresponding concave portion 70in the second direction D2 (for example, the deepest position on thebranch area 40 side). Although FIG. 4 shows that each concave portion 70is semicircular, the shape of each concave portion 70 is not limited tothis example.

In another respect, the second edge E2 of the axial area 30 comprises aplurality of convex portions 80 arranged in the second direction D2.Each convex portion 80 is aligned with a corresponding gap area 60 inthe first direction D1. For example, the center of each gap area 60 inthe second direction D2 may match the center of a corresponding convexportion 80 in the second direction D2 (for example, the projectingposition closest to the extension area 50).

In the present embodiment, the axial area 30 and each branch area 40 areareas in which the second common electrode CE2 is not present, and thepixel electrode PE is present. Thus, the second edge E2 is equivalent tothe edge of the pixel electrode PE on the video signal line S2 side.Each gap area 60 is an area in which the second common electrode CE2 ispresent. The extension area 50 is an area in which the second commonelectrode CE2 and the pixel electrode PE are not present, and the firstcommon electrode CE1 is present. Thus, each concave portion 70 (moreprecisely, the extension area 50 on the internal side of each concaveportion 70) is an area in which the second common electrode CE2 and thepixel electrode PE are not present, and the first common electrode CE1is present. The other area is an area in which the second commonelectrode CE2 is present. In this structure, the axial area 30 and eachbranch area 40 have pixel potential, and the other area has commonpotential.

Alignment treatment is applied to the first alignment film 14 and thesecond alignment film 24 shown in FIG. 3 in an alignment treatmentdirection AD parallel to the first direction D1. Thus, the first andsecond alignment films 14 and 24 have a function for causing the liquidcrystal molecules to be aligned in the initial alignment directionparallel to the alignment treatment direction AD. In the presentembodiment, the extension directions of the branch areas 40 and the gapareas 60 are identical with the initial alignment direction of theliquid crystal molecules.

Now, this specification explains the details of the shapes of the axialarea 30 and the branch areas 40 which have pixel potential. FIG. 6 is apartial enlarged view of the axial area 30 and each branch area 40 shownin FIG. 4. Each branch area 40 comprises a first side 41 and a secondside 42 in the second direction D2. Each branch area 40 furthercomprises a top side 43 connecting the first side 41 and the second side42 at the distal end. The axial area 30 comprises a bottom side 31between two adjacent branch areas 40. Each first side 41 is inclined atan angle θ which is an acute angle in a counterclockwise direction (forexample, approximately 1 degree) with respect to the alignment treatmentdirection AD. Each second side 42 is inclined at the angle θ in aclockwise direction with respect to the alignment treatment directionAD.

A corner C1 is formed by the bottom side 31 and the first side 41. Acorner C2 is formed by the first side 41 and the top side 43. A cornerC3 is formed by the bottom side 31 and the second side 42. A corner C4is formed by the second side 42 and the top side 43.

The axial area 30 comprises connective areas 32 connected to the branchareas 40, and non-connective areas 33 adjacent to the gap areas 60 inthe first direction D1. The connective areas 32 and the non-connectiveareas 33 are alternately arranged in the second direction D2. Eachconcave portion 70 is formed in a corresponding connective area 32. Bendportions BP1 and BP2 are formed at the both ends of each concave portion70 (in other words, at the boundaries between each concave portion 70and corresponding convex portions 80). In the example of FIG. 6, boththe bend portion BP1 and the bend portion BP2 are located in theconnective areas 32. As another example, the bend portions BP1 and BP2may be located on the extensions of the first and second sides 41 and 42of the branch areas 40. Alternatively, the bend portions BP1 and BP2 maybe located in the non-connective areas 33.

The length of each connective area 32 in the second direction D2 is L1.The length of each non-connective area 33 in the second direction D2 isL2. In the example of FIG. 6, length L1 is greater than length L2(L1>L2). However, length L1 may be less than or equal to length L2(L1≤L2).

The length (depth) of each concave portion 70 in the first direction D1is L3. Length L3 is also equivalent to the length (height) of eachconvex portion 80 in the first direction D1. The length (width) of eachnon-connective area 33 in the first direction D1 is L4. The maximumlength of each connective area 32 in the first direction D1 is also L4.For example, length L3 is preferably greater than or equal to 1 μm.Length L3 is preferably greater than or equal to one-third of length L4(L3≥L4/3).

The length of each branch area 40 in the first direction D1 is L5. Eachbranch area 40 is an area which substantially contributes to display. Asdescribed above, the axial area 30 overlaps the light-shielding layer21. Thus, when length L4 is much greater than length L5, the area whichdoes not contribute to display is increased. In this way, the displayquality is reduced. From this aspect, length L4 is preferably less thanor equal to one-fifth of the sum of length L4 and length L5(L4≤(L4+L5)/5).

The present embodiment allows the realization of a high-speed responsemode in which the response is faster than that of the common FFS mode.The speed of response can be defined as, for example, the speed when thephototransmittance of the liquid crystal layer LC is changed betweenpredetermined levels by the voltage application between the pixelelectrodes PE and the common electrode CE (specifically, the first andsecond common electrodes CE1 and CE2).

Now, this specification explains the operation principle of thehigh-speed response mode with reference to FIG. 7 and FIG. 8.

FIG. 7 shows a part of the axial area 30 and the branch areas 40, andthe initial alignment state of the liquid crystal molecules LM includedin the liquid crystal layer LC. As shown in FIG. 7, the liquid crystalmolecules LM are initially aligned such that the long axis conforms tothe alignment treatment direction AD in an off-state where no voltage isapplied between the pixel electrode PE and the common electrode CE(specifically, the first and second common electrodes CE1 and CE2).

In the common FFS mode which is widely used, all the liquid crystalmolecules rotate in the same direction when a fringe electric field isformed between two electrodes. However, the rotation of the liquidcrystal molecules in high-speed response mode is different from that ofthe liquid crystal molecules in FFS mode.

FIG. 8 shows the alignment state of the liquid crystal molecules LM inan on-state where voltage is applied between the pixel electrode PE andthe common electrode CE (specifically, the first and second commonelectrodes CE1 and CE2). The lines EL1 and EL2 shown in FIG. 8 areexamples of the equipotential lines of the electric field generatedaround the axial area 30 and the branch areas 40. In the liquid crystalmolecules LM of the present embodiment, the dielectric anisotropy ispositive. Therefore, when voltage is applied between the pixel electrodePE and the common electrode CE (specifically, the first and secondcommon electrodes CE1 and CE2) in the off-state shown in FIG. 7, forceis applied to rotate the liquid crystal molecules LM such that the longaxis is made parallel to the direction of the electric field generatedby the application of voltage (or is made perpendicular to theequipotential lines EL1 and EL2).

The liquid crystal molecules LM rotate in a first rotational directionR1 indicated with the solid arrows near the corners C1 and C2. Theliquid crystal molecules LM rotate in a second rotational direction R2indicated with the dashed arrows near the corners C3 and C4. The firstrotational direction R1 and the second rotational direction R2 aredifferent from (opposite to) each other.

The corners C1 to C4 have a function for controlling the alignment (inother words, a function for stabilizing the alignment) by controllingthe rotational direction of the liquid crystal molecules LM near thefirst and second sides 41 and 42. The liquid crystal molecules LM nearthe first sides 41 rotate in the first rotational direction R1 inconnection with the rotation of the liquid crystal molecules LM nearcorners C1 and C2. The liquid crystal molecules LM near the second sides42 rotate in the second rotational direction R2 in connection with therotation of the liquid crystal molecules LM near the corners C3 and C4.Near the center of each branch area 40 and the center of each gap areaGO in the second direction D2, the liquid crystal molecules LM rotatingin the first rotational direction R1 compete with the liquid crystalmolecules LM rotating in the second rotational direction R2. Thus, theliquid crystal molecules LM in these areas are maintained in the initialalignment state, and hardly rotate.

As described above, in high-speed response mode, the rotationaldirections of the liquid crystal molecules LM are aligned from theproximal sides to the distal sides near the first and second sides 41and 42. Thus, when voltage is applied, a response can be made fast.Moreover, the rotational directions of the liquid crystal molecules LMcan be uniform. Thus, it is possible to improve the stability ofalignment.

In the branch areas 40, the first and second sides 41 and 42 areinclined with respect to the alignment treatment direction AD. Thisstructure also contributes to the improvement of the stability ofalignment. Near the first and second sides 41 and 42 inclined withrespect to the alignment treatment direction AD, the direction of theelectric field intersects the alignment treatment direction AD at anangle other than a right angle. Thus, it is possible to cause therotational direction of the liquid crystal molecules LM to besubstantially constant when voltage is applied.

Now, this specification explains the vicinity of the second edge E2 ofthe axial area 30. As described above, the second edge E2 comprises theconcave portions 70 and the convex portions 80. The equipotential lineEL2 meander in accordance with the shapes of the concave portions 70 andthe convex portions 80. From the bend portions BP1 and BP2 to the centerof each concave portion 70 in the second direction D2, the equipotentialline EL2 is inclined in a direction intersecting the first and seconddirections D1 and D2. In this way, the liquid crystal molecules LMrotate in the first rotational direction R1 near the bend portions BP1,and rotate in the second rotational direction R2 near the bend portionsBP2. Near the center of each concave portion 70 and the center of eachconvex portion 80 in the second direction D2, the liquid crystalmolecules LM rotating in the first rotational direction R1 compete withthe liquid crystal molecules LM rotating in the second rotationaldirection R2. Thus, the liquid crystal molecules LM in these areas aremaintained in the initial alignment state, and hardly rotate.

When the liquid crystal molecules LM near the second edge E2 rotate inthe above manner, the rotational directions of the liquid crystalmolecules LM are aligned from the first sides 41 to the bend portionsBP1. The rotational directions of the liquid crystal molecules LM arealigned from the second sides 42 to the bend portions BP2. Further, fromthe branch areas 40 to the concave portions 70, the liquid crystalmolecules LM do not rotate at the centers of the branch areas 40 and theconcave portions 70 in the second direction D2. Similarly, from the gapareas 60 to the convex portions 80, the liquid crystal molecules LM donot rotate at the centers of the gap areas 60 and the convex portions 80in the second direction D2.

FIG. 9 shows a comparison example of the present embodiment. In thiscomparison example, it is assumed that the second edge E2 of the axialarea 30 is flat in the second direction D2. In this case, theequipotential line EL2 is parallel to the second direction D2 over theentire second edge E2. Since the equipotential line EL2 is perpendicularto the alignment treatment direction AD, the liquid crystal molecules LMnear the second edge E2 are in an unstable state where the liquidcrystal molecules LM could rotate in both the first rotational directionR1 and the second rotational direction R2. For example, each electrodeis small in very fine pixels. Thus, the first and second rotationaldirections R1 and R2 of the liquid crystal molecules LM near the secondedge E2 are more easily unstable.

If the liquid crystal molecules LM near the extensions of the firstsides 41 rotate in the second rotational direction R2, the rotationaldirections of the liquid crystal molecules are not aligned between thevicinity of the first sides 41 and the vicinity of the second edge E2.Similarly, if the liquid crystal molecules LM near the extensions of thesecond sides 42 rotate in the first rotational direction R1, therotational directions of the liquid crystal molecules are not alignedbetween the vicinity of the second sides 42 and the vicinity of thesecond edge E2. When the rotational directions are not aligned in thisway, the speed of response is decreased near the first and second sides41 and 42.

However, when the concave portions 70 or the convex portions 80 areprovided in the second edge E2 such that the equipotential line EL2 iscurved as shown in FIG. 8, the rotational directions of the liquidcrystal molecules LM are aligned from the vicinity of the first andsecond sides 41 and 42 to the vicinity of the second edge E2. In thisway, the speed of response in high-speed response mode can be furtherincreased.

By increasing the speed of response, the image displayed by the displaydevice 1 is swiftly switched. Thus, various excellent effects can beobtained. For example, an image can be displayed with high quality.

In the present embodiment, an area having pixel potential and an areahaving common potential are formed in each subpixel SP by usingelectrodes (PE, CE1 and CE2) formed in three different layers. Theeffect of this structure is explained with reference to FIG. 4 and FIG.10.

FIG. 10 shows a comparison example of the present embodiment. Thiscomparison example is different from the present embodiment in respectthat the comparison example comprises a two-layer structure includingthe layer of a common electrode CEa and the layer of pixel electrodesPEa. The common electrode CEa comprises an aperture A12 a for eachsubpixel SP. The aperture A12 a overlap the pixel electrodes PEa as seenin plan view. Each aperture A12 a comprises an axial area 30 a, aplurality of branch areas 40 a extending from the axial area 30 a, aplurality of concave portions 70 a and a plurality of convex portions 80a. In this comparison example, when very fine subpixels SP are provided,as shown in the arrows in FIG. 10, distance W0 between the distal end ofeach gap area 60 a and the concave portion 70 a near the gap area 60 ais short. Thus, they may be short-circuited. In particular, thispossibility is increased in the subpixels SP of a high-definitiondisplay device (for example, with 700 ppi or greater).

In the present embodiment, the internal side of each concave portion 70(in other words, the extension area 50) and each gap area 60 are formedby the first common electrode CE1 and the second common electrode CE2provided in different layers, respectively. Thus, even when distance W1shown with the arrows in FIG. 4 is short, the above short circuit doesnot occur. In another respect, each concave portion 70 can have asufficient depth. In this way, it is possible to further improve thestability of alignment.

Since the extension area 50 is provided, as shown with the arrows inFIG. 4, distance W2 between the distal end of each gap area 60 and theedge of the aperture A12 on the video signal line S2 side can be long.Specifically, even when distance W2 is long in this manner, the lengthof the axial area 30 in the first direction D1 can be decreased by theprovision of the extension area 50. In the three-layer structure, evenwhen distances W1 and W2 are long, the interference or short circuitbetween adjacent pixel electrodes PE can be reduced. Thus, very finesubpixels SP can be easily realized. Further, the relationships oflengths L1 to L5 explained with reference to FIG. 6 can be easilyrealized.

In addition to the above effects, the present embodiment can improve theflexibility of designing in terms of various aspects related to theshapes of the electrodes of the subpixels SP.

The shapes of each axial area 30, each branch area 40, each extensionarea 50, each gap area 60, each concave portion 70 and each convexportion 80 may be modified in various ways.

For example, each concave portion 70 and each convex portion 80 may bepolygonal. For example, they may be triangular or trapezoidal. Eachconcave portion 70 may have a shape similar to the distal end of eachbranch area 40. Similarly, each convex portion 80 may have a shapesimilar to the distal end of each gap area 60. In this disclosure, theterm “similarity” includes the meaning in which two objects merelyresemble each other in shape in addition to the geometric meaning inwhich, when one of two objects is reduced or enlarged, the objectcoincides precisely with the other object.

For example, as shown in FIG. 11, the axial area 30, each branch area40, the extension area 50, each gap area 60, each concave portion 70 andeach convex portion 80 may have a smooth outline. In the example of FIG.11, the distal end of each branch area 40 and each gap area 60 isarcuate. The boundaries between the concave portions 70 and the convexportions 80 are also smooth. In this way, the second edge E2 of theaxial area 30 is arcuate such that it smoothly meanders. In this case,the convex portions 80 are similar to the gap areas 60. The concaveportions 70 are similar to the distal ends of the branch areas 40. Forexample, the curvature of the distal ends of the branch areas 40 isgreater than the curvature of the concave portions 70. The curvature ofthe distal ends of the gap areas 60 is greater than the curvature of theconvex portions 80.

Second Embodiment

A second embodiment is explained. The same or similar elements as/tothose of the first embodiment are denoted by like reference numbers,detailed description thereof being omitted unless necessary. Thestructures which are not particularly referred to are the same as thoseof the first embodiment.

FIG. 12 shows a part of the cross-sectional surface of a display panel 2provided in a display device 1 according to the second embodiment. In amanner similar to that of FIG. 3, FIG. 12 shows the schematiccross-sectional view of a subpixel SP.

In the present embodiment, each pixel electrode PE includes a firstpixel electrode PE1 and a second pixel electrode PE2. In the firstembodiment, the display panel 2 comprises two common electrodes CE1 andCE2. However, in the present embodiment, the display panel 2 comprisesonly one common electrode CE.

The first pixel electrode PE1 is formed on a first insulating layer 11.The first pixel electrode PE1 is covered with a second insulating layer(first dielectric layer) 12. The common electrode CE is formed on thesecond insulating layer 12. The common electrode CE is covered with athird insulating layer (second dielectric layer) 13. The second pixelelectrode PE2 is formed on the third insulating layer 13. The secondpixel electrode PE2 is covered with a first alignment film 14. The firstpixel electrode PE1 is connected to a switching element SW via a contacthole H21 penetrating the first insulating layer 11. The second pixelelectrode PE2 is connected to the first pixel electrode PE1 via acontact hole H22 penetrating the second and third insulating layers 12and 13 and an aperture A21 provided in the common electrode CE. Thefirst and second pixel electrodes PE1 and PE2 and the common electrodeCE can be formed of a transparent conductive material such as ITO.

FIG. 13 is a plan view schematically showing an example of a subpixel SPaccording to the present embodiment. FIG. 14A, FIG. 14B and FIG. 14C arethe schematic plan views of the first pixel electrode PE1, the commonelectrode CE and the second pixel electrode PE2 shown in FIG. 13,respectively.

In the examples of FIG. 13 and FIG. 14A, the most part of the firstpixel electrode PE1 is provided in the area surrounded by scanning linesG1 and G2 and video signal lines S1 and S2. In addition, the first pixelelectrode PE1 extends in the area on the left side of the video signalline S1. The first pixel electrode PE1 may be provided within the areasurrounded by the scanning lines G1 and G2 and the video signal lines S1and S2.

As shown in FIG. 13 and FIG. 14B, the common electrode CE is formed overa plurality of subpixels SP. The common electrode CE comprises anaperture A22 in addition to the above aperture A21. The above contacthole H22 is provided at a position overlapping the aperture A21 as seenin plan view. Although the aperture A22 overlaps the adjacent subpixelarea, the overlapping position is covered with a light-shielding layer21. Thus, even if the electric field in a subpixel area has a slighteffect on the alignment of the liquid crystal molecules in anothersubpixel area, the effect does not cause a large problem.

As shown in FIG. 13 and FIG. 14C, the second pixel electrode PE2 isprovided in the area surrounded by the scanning lines G1 and G2 and thevideo signal lines S1 and S2. The second pixel electrode PE2 may extendto the outside of this area.

For example, the first pixel electrode PE1 overlaps the common electrodeCE excluding the apertures A21 and A22. For example, the commonelectrode CE overlaps the entire second pixel electrode PE2. However,the second pixel electrode PE2 may comprise a portion which does notoverlap the common electrode CE.

In each subpixel SP of the present embodiment, similarly, an axial area30, a plurality of branch areas 40 and a plurality of gap areas 60 areprovided. The axial area 30 and each branch area 40 have pixelpotential. The other area including each gap area 60 has commonpotential. The axial area 30 comprises a first edge E1 on the videosignal line S2 side, and a second edge E2 on the video signal line S1side. Each branch area 40 extends from the first edge E1 of the axialarea 30 to the video signal line S2 in a first direction D1.

The axial area 30 includes a first portion P1 on the video signal lineS2 side, and a second portion P2 on the video signal line S1 side. Thefirst portion P1 comprises the first edge E1. The second portion P2comprises the second edge E2. Both the first portion P1 and the secondportion P2 extend in a second direction D2. In the example of FIG. 13,the second portion P2 is shorter than the first portion P1 in the seconddirection D2. However, the first and second portions P1 and P2 may havethe same length. Alternatively, the second portion P2 may be longer thanthe first portion P1. Both ends of the first and second portions P1 andP2 in the second direction D2 may be aligned or may not be aligned.

The second edge E2 of the axial area 30 (in other words, the edge of thesecond portion P2) comprises a plurality of convex portions 80 arrangedin the second direction D2. Each convex portion 80 is aligned with acorresponding gap area 60 in the first direction D1. For example, thecenter of each gap area 60 in the second direction D2 may match thecenter of a corresponding convex portion 80 in the second direction D2(in other words, the most projecting position). Although FIG. 13 showsthat each convex portion 80 is semicircular, the shape of each convexportion 80 is not limited to this example.

In another respect, the second edge E2 of the axial area 30 comprises aplurality of concave portions 70 arranged in the second direction D2.Each concave portion 70 is aligned with a corresponding branch area 40in the first direction D1. For example, the center of each branch area40 in the second direction D2 may match the center of a correspondingconcave portion 70 in the second direction D2 (in other words, thedeepest position on the branch area 40 side).

The aperture A22 of the common electrode CE includes the second portionP2 and the convex portions 80. As seen in plan view, the edge of theaperture A22 on the video signal line S2 side matches the edge of thesecond pixel PE2 on the video signal line S1 side, or is located betweenthe edge of the second pixel electrode PE2 on the video signal line S1side and the first edge E1.

In the present embodiment, the first portion P1 of the axial area 30 andeach branch area 40 are an area in which the second pixel electrode PE2is present. Each gap area 60 is an area in which the second pixelelectrode PE2 is not present, and the common electrode CE is present.The second portion P2 of the axial area 30 is an area in which thesecond pixel electrode PE2 and the common electrode CE are not present,and the first pixel electrode PE1 is present. Thus, each convex portion80 (more precisely, the second portion P2 on the internal side of eachconvex portion 80) is an area in which the second pixel electrode PE2and the common electrode CE are not present, and the first pixelelectrode PE1 is present. The other area is an area in which the secondpixel electrode PE2 is not present, and the common electrode CE ispresent. In this structure, the axial area 30 and each branch area 40have pixel potential, and the other area has common potential.

Alignment treatment is applied to the first alignment film 14 and thesecond alignment film 24 shown in FIG. 12 in an alignment treatmentdirection AD parallel to the first direction D1. In the presentembodiment, in a manner similar to that of the first embodiment, theextension directions of the branch areas 40 and the gap areas 60 areidentical with the initial alignment direction of the liquid crystalmolecules. In the liquid crystal molecules of the liquid crystal layerLC, the dielectric anisotropy is positive.

The same structures as the first embodiment, for example, therelationships of lengths L1 to L5 shown in FIG. 6, may be applied to theshapes of each axial area 30, each branch area 40 and each gap area 60.The various shapes explained in the first embodiment may be applied tothe shapes of each concave portion 70 and each convex portion 80. Forexample, in a manner similar to that of the example shown in FIG. 11,the axial area 30, each branch area 40, the extension area 50, each gaparea 60, each concave portion 70 and each convex portion 80 may have asmooth outline.

In the structure of the above embodiment, as explained with reference toFIG. 7 and FIG. 8, it is possible to obtain the display device 1 inhigh-speed response mode in which the speed of response and thestability of alignment are improved.

When the convex portions 80 are provided in the axial area 30 like thepresent embodiment, as shown with the arrows in FIG. 13, distance W3between the distal end of each branch area 40 of a subpixel SP and acorresponding convex portion 80 of the adjacent subpixel SP is short. Ifthe branch areas 40 and the convex portions 80 are formed in the sameconductive layer, and distance W3 is short, they may be short-circuited.In particular, this possibility is increased in very fine subpixels SP.However, in the present embodiment, each branch area 40 and each convexportion 80 are formed by the first pixel electrode PE1 and the secondpixel electrode PE2 provided in different layers, respectively. Thus,even if distance W3 is short, the above short circuit does not occur. Inanother respect, each convex portion 80 can have a sufficient height. Inthis way, it is possible to further improve the stability of alignment.

In addition to the above description, the same effects as the firstembodiment can be obtained from the present embodiment.

In the present embodiment, the axial area 30 includes the first portionP1 and the second portion P2. However, the axial area 30 may not includethe second portion P2. FIG. 15 shows an example of the plane shape ofthe common electrode CE which can be applied in this case. In theexample of FIG. 15, the common electrode CE comprises a plurality ofapertures A23 arranged in the second direction D2. As seen in plan view,the apertures A23 are in contact with the axial area 30 (the secondportion P2 of the second pixel electrode PE2). In this case, the firstpixel electrode PE1 (not shown in FIG. 15) exposed from the aperturesA23 are connected to the axial area 30. As a result, the convex portions80 of the axial area 30 are formed.

Each embodiment discloses a structure which can be adopted when thedielectric anisotropy of the liquid crystal molecules of the liquidcrystal layer LC is positive. However, the liquid crystal layer LC maybe structured by liquid crystal molecules in which the dielectricanisotropy is negative. In this case, the alignment treatment directionAD (or the initial alignment direction of liquid crystal molecules) maybe a direction (second direction D2) perpendicular to the extensiondirection (first direction D1) of the branch areas 40.

All of the display devices which may be realized by a person of ordinaryskill in the art by appropriately changing the design based on thedisplay device explained as each embodiment of the present inventionfall within the scope of the present invention as long as they encompassthe spirit of the invention.

Various modification examples which may be conceived by a person ofordinary skill in the art in the scope of the idea of the presentinvention will also fall within the scope of the invention. For example,even if a person of ordinary skill in the art arbitrarily modifies theabove embodiments by adding or deleting a structural element or changingthe design of a structural element, or adding or omitting a step orchanging the condition of a step, all of the modifications fall withinthe scope of the present invention as long as they are in keeping withthe spirit of the invention.

Further, other effects which may be obtained from the embodiments andare self-explanatory from the descriptions of the specification or canbe arbitrarily conceived by a person of ordinary skill in the art areconsidered as the effects of the present invention as a matter ofcourse.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a second substrate; and a liquid crystal layer providedbetween the first substrate and the second substrate, and includingliquid crystal molecules, wherein the first substrate comprises: aplurality of subpixels; a first pixel electrode provided for each of thesubpixels, and having pixel potential; a second pixel electrode betweenthe first pixel electrode and the liquid crystal layer, provided foreach of the subpixels, and having pixel potential; and a commonelectrode between the first pixel electrode and the second pixelelectrode, and having common potential, each of the subpixels comprises:an axial area comprising first and second edges arranged in a firstdirection, and extending in a second direction intersecting the firstdirection; a plurality of branch areas extending from the first edge ofthe axial area in the first direction; and a plurality of gap areasbetween the branch areas, the second edge comprises a plurality ofconvex portions arranged in the second direction, the branch areas areareas in which the second pixel electrode is present, the gap areas areareas in which the second pixel electrode is not present, and the commonelectrode is present, and the convex portions are areas in which thesecond pixel electrode and the common electrode are not present, and thefirst pixel electrode is present.
 2. The liquid crystal display deviceof claim 1, wherein the common electrode comprises an aperture having ashape including the convex portions.
 3. The liquid crystal displaydevice of claim 1, wherein the axial area includes a first portioncomprising the first edge, and a second portion comprising the secondedge, the first portion is an area in which the second pixel electrodeis present, the second portion is an area in which the common electrodeand the second pixel electrode are not present, and the first pixelelectrode is present, and the convex portions are provided in the secondportion.
 4. The liquid crystal display device of claim 1, wherein theaxial area includes a connective area connected to the branch areas, anda non-connective area adjacent to the gap areas, and a width of thenon-connective area in the first direction is less than or equal toone-fifth of a total width of the connective area and each of the branchareas in the first direction.
 5. The liquid crystal display device ofclaim 4, wherein a width of the non-connective area in the seconddirection is greater than a width of the connective area in the seconddirection.
 6. The liquid crystal display device of claim 1, wherein eachof the branch areas comprises first and second sides arranged in thesecond direction, and when an electric field for rotating the liquidcrystal molecules is generated, a rotational direction of the liquidcrystal molecules differs between a vicinity of the first side and avicinity of the second side.
 7. The liquid crystal display device ofclaim 1, wherein the convex portions are aligned with the gap areas inthe first direction.
 8. The liquid crystal display device of claim 1,wherein the second substrate comprises a light-shielding layeroverlapping the axial area as seen in plan view.
 9. The liquid crystaldisplay device of claim 8, wherein the light-shielding layer overlaps adistal portion and a proximal portion of each of the branch areas asseen in plan view.
 10. The liquid crystal display device of claim 1,wherein a length of each of the convex portions in the first directionis greater than or equal to one-third of a length of the axial area inthe first direction.